I discover this today . First time i see the bug . When you skill the wings or back items will appear .

Req :
*Google Chrome
*Ninja Saga

Step :
1. Go To Shop .
2. Then Click Back Items .
3. Click the back item worth 10k or what you want to wear .
4. Then Exit
5. Play Pvp or Mission .
6. Then the Back item you click or wear will appear when you skill the enemy .